Where is the credit for the "Voluntary Federal Income Tax Withheld" from my SSA checks accounted for in form 1040-SR?

Taxes withheld are reported on a Form 1040 on Line 25.  Line 25a for taxes withheld on a W-2.  Line 25b for taxes withheld on a Form 1099 (such as a SSA-1099 and Form 1099-R)

Did you enter it in the right spot on the same screen as Social Security?  Social Security is on line 6a and any taxable amount on 6b. Any withholding will show up on 1040 line 25b.

To enter, edit or delete a form 1099-R -

Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Scroll down to Retirement Plans and Social Security
On IRA, 401(k), Pension Plan Withdrawals (1099-R), click the start or update button

Or enter 1099-r in the Search box located in the upper right of the program screen. Click on Jump to 1099-R

To enter Social Security benefits reported on form SSA-1099

Click on Federal Taxes (Personal using Home and Business)
Click on Wages and Income (Personal Income using Home and Business)
Click on I'll choose what I work on (if shown)
Scroll down to Retirement Plans and Social Security
On Social Security (SSA-1099, RRB-1099), click the start or update button

Or enter ssa-1099 in the Search box located in the upper right of the program screen. Click on Jump to ssa-1099